1. Field of the Invention
The present invention relates to a recording medium represented by an optical disk optically rewritable, an access device and an access method. More particularly, the present invention relates to an optical disk which enables a quick random access operation if the disk is formed into a large capacity, an access device and an access method.
2. Description of Related Art
Conventionally, there is a recording medium provided with data identification information for each information unit of a predetermined data length in order to carry out a random access operation to data on a medium. The typical examples are such optical disks as magneto optic disk (hereinafter referred to as MO) using magneto optic recording and DVD disk (hereinafter referred to as DVD), which uses a change in phase of the medium. These optical disks are used as a large-scale external recording medium for computer. Additionally, they are used for recording visual information such as movie. As the computer has handled larger and larger data or higher-quality, longer-hour visual recording has been demanded, a further larger capacity has been demanded.
An optical disk 100 based on the conventional art shown in FIG. 9 is so constructed that information unit group constituted of plural information units are composed of tracks T100, which are formed of each single circle, the tracks being formed spirally. Each track T100 is divided to sectors S100 as information unit, which has a predetermined data length, so that data recording format is constructed. In an enlarged view of four tracks 100A on the optical disk 100 shown in FIG. 9, the sector S100 comprises data portion 120 which is a region in which data is to be written and control information portion 110, which includes ID portion 112 as data identification information for identifying the content of the data portion 120 and a sector mark portion 111 which is recognition information for recognizing the start position of the sector S100.
FIG. 10 shows an enlarged view of the bit structure on a boundary region of the control information portion 110 and data portion 120 on the optical disk 100. Referring to FIG. 10, data is recorded on only land L100 on the data portion 120 of the optical disk 100. In the meantime, although not indicated, data may be recorded in only the groove G100. Here, each data bit pattern 125 in the data portion 120 is a rewritable data pattern, which is constructed by magneto optic recording in case of MO or phase change recording in case of DVD. Contrary to this, the sector mark portion 111 on the control information portion 110 and each control information bit pattern 115 on the ID portion 112 are uneven patterns processed in the disk 100 by etching or the like, that is, a fixed pattern constituted of so-called emboss pit pattern.
As for the data bit pattern 125, as compared to beam spot such as pick-up laser beam or the like, even if the bit pattern size or the bit pattern pitch is miniaturized, data reading corresponding to highly integration of the data bit pattern 125 is enabled by development of so-called magnetic super-resolution (MSR) technology or the like, which reads out by using temperature distribution in a beam spot.
Next, FIG. 11 shows a high-density optical disk 200 in case where the data portion 220 is formed in high density. An enlarged view of four tracks 200A like the case of FIG. 9 is shown here. The high-density optical disk 200 adopts a land groove recording type as shown in FIG. 12 for integration into a higher density. The data bit pattern 125 (see FIG. 10), which has conventionally been recorded in only the land L100 or the groove G100, is recorded both in the land L200 and groove G200 by narrowing the bit pattern pitch using magnetic super-resolution (MSR) technology and the like. Thus, as compared to a case where the track T100 is constituted of any one of the land L100 or the groove G100 (see FIGS. 9, 10), the quantity of the tracks T200 constituted of both the land L200 or the groove G200 is doubled thereby achieving high density.
However, because in case of the control bit pattern 115, 215, the bit pattern is formed with the emboss pit pattern at the time of manufacturing the optical disk 100 and the high density optical disk 200 as compared to the data bit patterns 125, 225, processing accuracy in manufacturing process needs to be improved for miniaturization and however, the miniaturization has not been progressed. Therefore, the pitch of the track T100 on which the data bit pattern 125 is to be recorded in the optical disk 100 is specified by the size of the emboss pit pattern of the control bit pattern 115, so that achievement of high density cannot be attained, which is a problem to be solved.
In the high-density optical disk 200 intending to achieve high density shown in FIG. 11, a control information portion 210 is assigned to a two-truck width consisting of two lands L200 and two grooves G200 and the control information portion 210 and the two-truck width are arranged in a row. That is, subsequent to a sector mark portion 211, two ID portions 212, 213 are arranged in line to record. In the data portion 220, the ID portion 212 is allocated as data identification information of the data 222 and the ID portion 213 is allocated as data identification information of the data 223. With miniaturization of the data bit pattern 225 in the high density optical disk 200, the overhead of the control information portion 210 in the track T200 is increased, thereby obstructing intensification in the density of the high density optical disk 200, which is a problem to be solved.
Further, to achieve miniaturization in the emboss pit pattern of the controlling bit patterns 115, 215 in the control information portions 110, 210, the processing accuracy in manufacturing process needs to be improved thereby inducing an increase in production cost.
Further, if the size of the emboss pit pattern in the controlling bit pattern 115, 215 is miniaturized, it is necessary to use short wavelength laser such as blue laser as the wavelength of a pick-up laser beam, inducing an increase in part cost.
To reduce the overhead of the control information portion 210 in the high-density optical disk 200, it can be considered to adopt a method of sharing the ID portion for multiple sectors instead of the ID portions 212, 213 provided for each sector as the data identification information. However, in this case, if a beam spot of laser or the like suffers from a positional error generated from a normal access position, detection of normal access position is disabled or it takes an extremely long time for the detection, so that there is a fear that an access to a mistaken position may be made, which is a problem to be solved.